1. Field of the Invention
The present invention relates to a heat-sensitive recording material. More particularly, the present invention relates to a heat-sensitive recording material having not only an excellent image and color-forming property, recording property and storing durability, but also an enhanced gloss on the recording face thereof.
2. Description of the Related Arts
It is known that a conventional heat-sensitive recording material comprises a substrate material, for example, a paper sheet, synthetic paper sheet, or a plastic resin film, and a heat-sensitive color-forming layer formed on a surface of the substrate material and comprising a substantially colorless dye precursor consisting of, for example, an electron-donative leuco basic dye, a color-developing agent consisting of an organic acid material, for example, an electron-acceptive phenolic compound, and a binder, and the colored recording images can be formed by reacting the dye precursor with the color-developing agent upon applying a heat energy.
This type of heat-sensitive recording material is advantageous in that colored images can be easily formed only by heating imagewise and the recording apparatus can be made relatively compact and in a small size at a low cost, and easily maintained, and thus are widely utilized as information-recording materials for various printers used with, for example, computers, facsimile machines, automatic ticket-vending machines, scientific measurement recorders, and CRT medical measurement recorders.
Nevertheless, the conventional heat-sensitive recording materials in which only the heat-sensitive color-forming layer comprising the dye precursor, the color-developing agent and the binder is directly formed on the substrate material is disadvantageous in that the heat-sensitive color-forming layer is unstable with respect to light, water, heat, plasticizing agents and oily substances, and thus deteriorates in quality with a lapse of time. Also, the conventional heat-sensitive recording materials are disadvantageous in that, when a colored image-forming operation is applied to the heat-sensitive color-forming layer the resultant image-formed portions and the non-image-formed portions in the layer have a relatively low gloss, because the heat sensitive color-forming layer is directly exposed to the outside.
To improve the storage stability of the conventional heat-sensitive recording materials, various attempts have been made to coat the surface of the heat-sensitive color-forming layer with a specific coating layer. For example, Japanese Unexamined Patent Publication No. 56-146,794 discloses the coating of the surface of the heat-sensitive color-forming layer with an aqueous emulsion of a hydrophobic polymeric compound, to thereby form a surface-covering layer.
Also, Japanese Unexamined Patent Publication No. 58-199,189 discloses an improved heat-sensitive recording material in which an upper surface of a heat-sensitive color-forming layer is coated with an aqueous solution of a water-soluble polymeric compound or an aqueous emulsion of a hydrophobic polymeric compound to form an intermediate layer, and the intermediate layer surface is coated with an oily paint comprising, as a resinous component, a hydrophobic polymeric compound, to thereby form a surface-covering layer.
Where the above-mentioned surface-covering layer is formed, it was found that, when the resultant heat-sensitive recording materials are brought into contact with a thermal head of a printer to form colored images thereon, sometimes the thermal head is adhered to the surface of the recording material. Therefore, the above-mentioned heat-sensitive recording materials do not have a satisfactory recording operability. Especially, in the case of video printers by which colored images having a high degree of harmony are to be recorded, an adhesion of the recording material to the thermal head must be prevented.